Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
Case	Tag   Price	Sales   Tax %	Raw Total   Incl. Sales Tax	Rounded   to Penny	Rounded   to Nickel	Rounded   to Dime
Purchase #1	$34.69	13.289%	$39.3	$39.30	$39.30	$39.30
Purchase #2	$80.29	12.561%	$90.3752	$90.38	$90.40	$90.40
Purchase #3	$173.84	4.623%	$181.8766	$181.88	$181.90	$181.90
Purchase #4	$117.30	11.716%	$131.0429	$131.04	$131.05	$131.00
Purchase #5	$167.94	11.812%	$187.7771	$187.78	$187.80	$187.80
Purchase #6	$10.25	9.660%	$11.2402	$11.24	$11.25	$11.20
Purchase #7	$235.87	11.347%	$262.6342	$262.63	$262.65	$262.60
7 purchase totals =	$820.18		$904.2462	$904.25	$904.35	$904.20